1. Field of the Invention
The present invention relates generally to flowable fill materials capable of forming stable backfills and to controlled low-strength mixtures which are initially fluid, self-leveling and which can be placed in the earth in various earth filling operations.
2. Description of the Prior Art
Controlled Low-Strength Mixtures (CLSMs), or flowable back-fills, were first developed in the early 1970s. Such materials have been used, for example, to fill narrow or remote trenches in the earth, as pipe bedding materials. A material process was patented by the Detroit Edison Company, of Detroit, Mich., which produced what was then called a controlled density fill (CDF) marketed as K-KRETE. K-KRETE exhibited a relatively low strength compared to conventional concrete, about 100 psi or less, but enjoyed some commercial success. Several similar products were marketed under the trade designations M-CRETE, S-CRETE, FLOWABLE FILL, FLASH FILL, ONE-SACK MIX, and FLOWABLE GROUT. These materials featured low cement contents, fine-graded aggregates, and easily handled liquid textures. One stabilized fill material marketed by the Detroit Edison Company is described in U.S. Pat. No. 4,374,672, issued Feb. 22, 1983. The product was comprised of 45-80% fly ash, 1-6% cement and 20-50% water. The material could be positioned under water to form a continuous causeway, or the like.
The concrete industry has now set standards for the properties of CLSMs. As compared to other types of construction materials, these materials have been tentatively designed as having set compressive strengths after 21 days of 1200 psi or less, and are commonly required to have strengths less than 300 psi to be considered easily removable.
Controlled Low-Strength Mixtures are used largely for a variety of structural and protective applications. A CLSM is typically very fluid, and therefore is self-leveling and easy to place in narrow or remote trenches. As they are self-setting and hardening, CLSMs also eliminate the need to refill trenches in an expensive and labor-intensive thin-layer process. The ingredient flexibility in CLSM mix designs permits their customization for thermal or noise insulation needs, as well.
The controllable properties of CLSMs have also made them a preferred pipe bedding. CLSMs do not settle or shrink, and thus provide consistent, durable support for large, expensive sewer pipes placed within them. The fill will also serve as a ballast and water barrier, protecting pipes from internal loads and external water damage.
The water resistance characteristics of CLSMs make them suitable candidates for erosion and environmental control projects. Numerous embankments and stilling basins have been lined with CLSM, as well as culvert and abutments about old bridges.
A need exists therefore for a CLSM which does not require mechanical compaction, which can be provided as a liquid product and which can be handled as a liquid.
A need also exists for a CLSM which is self-hardening, requiring only that the composition be left in place to achieve the desired strength and mechanical properties.
One object of the present invention is to provide such a CLSM which does not contain cement or other self-setting adhesive products.
Another object of the invention is to provide a CLSM which can be poured into a confined space, such as a narrow trench, without premature setting or hardening.
Another object of the invention is to provide a CLSM which has homogeneous and consistent mechanical properties which exceed those of lime-soil mixtures alone.
Another object of the invention is to provide a CLSM which can be used as an insulating thermal fill.
Another object of the invention is to provide a CLSM which can be used as a moisture barrier in soil.
Another object of the invention is to provide a CLSM which can be used as a structural backfill in underground mining.